The role of the spiracles in gas exchange during development of Samia cynthia (Lepidoptera, Saturniidae).

Spiracles and the tracheal system of insects allow effective delivery of respiratory gases. During development, holometabolous insects encounter large changes in the functional morphology of gas exchange structures. To investigate changes in respiratory patterns during development, CO2-release was measured in larvae, pre-pupae and pupae of Samia cynthia (Lepidoptera, Saturniidae). Gas exchange patterns showed great variability. Caterpillars had high metabolic rates and released carbon dioxide continuously. Pre-pupae and pupae showed typical discontinuous gas exchange cycles (DGC) at reduced metabolic rates. Changes in gas exchange patterns can partly be explained with low metabolic rates during pupation. Sequential blocking of spiracles in pre-pupae and pupae reduced spiracle conductance with tracheal conductance remaining unaffected. Analysis of gas exchange patterns indicates that caterpillars and pre-pupae use more than 14 spiracles simultaneously while pupae only use 8 to 10 spiracles. Total conductance is not a simple multiple of single spiracles, but may be gradually adaptable to gas exchange demands. Surprisingly, moth pupae showed a DGC if all except one spiracle were blocked. The huge conductance of single spiracles is discussed as a pre-adaptation to high metabolic demands at the beginning and the end of the pupal as well as in the adult stage.     

Winter gas exchange between the atmosphere and snow-covered soils on Niwot Ridge,Colorado, USA

Background: There is a growing interest in understanding the gas exchange between the atmosphere and seasonally snow-covered regions, especially in light of projections that climate change will alter the timing and extent of seasonal snow cover. In snow-covered ecosystems, gas fluxes are due both to microbial activity in the snow-covered soils and to chemical and physical reactions with the various gases and/or dissolved constituents in the snowpack. Niwot Ridge, in the Colorado Rocky Mountains, has one of the most extensive sets of measurements of winter gas exchange globally.

Aims: Our goal was to examine the temporal patterns and environmental controls on Niwot Ridge of gas fluxes for gases with different sources and sinks.

Methods: Here, we review the concentrations and fluxes that have been measured for carbon dioxide, nitrous oxide, methane, nitrogen oxides, ozone, gaseous elemental mercury and volatile organic carbon compounds.

Results and Conclusions: We looked for similarities and differences among the gases, but in many cases, the origin, fate and controls of these fluxes still need to be determined. However, we believe that many of the biologically driven reactions are the result of exponential growth of a winter microbial community during the long period of stable environmental conditions under the seasonal snowpack.     

The role of the spiracles in gas exchange during development of Samia cynthia (Lepidoptera, Saturniidae)

Spiracles and the tracheal system of insects allow effective delivery of respiratory gases. During development, holometabolous insects encounter large changes in the functional morphology of gas exchange structures. To investigate changes in respiratory patterns during development, CO₂-release was measured in larvae, pre-pupae and pupae of Samia cynthia (Lepidoptera, Saturniidae). Gas exchange patterns showed great variability. Caterpillars had high metabolic rates and released carbon dioxide continuously. Pre-pupae and pupae showed typical discontinuous gas exchange cycles (DGC) at reduced metabolic rates. Changes in gas exchange patterns can partly be explained with low metabolic rates during pupation. Sequential blocking of spiracles in pre-pupae and pupae reduced spiracle conductance with tracheal conductance remaining unaffected. Analysis of gas exchange patterns indicates that caterpillars and pre-pupae use more than 14 spiracles simultaneously while pupae only use 8 to 10 spiracles. Total conductance is not a simple multiple of single spiracles, but may be gradually adaptable to gas exchange demands. Surprisingly, moth pupae showed a DGC if all except one spiracle were blocked. The huge conductance of single spiracles is discussed as a pre-adaptation to high metabolic demands at the beginning and the end of the pupal as well as in the adult stage.     

Apparatus for monitoring the oxygen uptake and carbon dioxide production of fermentations

The requirements of the continuous analysis of effluent gas streams from aerated flash and tank fermentors are described, as are instrumental devices for measuring the oxygen and carbon dioxide content of fermentor gases. The use of a specially designed sequential gas sample for monitoring four fermentations simultaneously and a system for precise control of low air flow and pressure is explained. Equations for calculating carbon dioxide production or oxygen consumption rates and respiratory quotients are given. A discussion of the operating characteristics of a device for automatic translation of aeration data between fermentors is presented.     

Endophytic strains of Trichoderma increase plants’ photosynthetic capability

The world faces two enormous challenges that can be met, at least in part and at low cost, by making certain changes in agricultural practices. There is need to produce enough food and fibre for a growing population in the face of adverse climatic trends, and to remove greenhouse gases to avert the worst consequences of global climate change. Improving photosynthetic efficiency of crop plants can help meet both challenges. Fortuitously, when crop plants’ roots are colonized by certain root endophytic fungi in the genus Trichoderma, this induces up-regulation of genes and pigments that improve the plants’ photosynthesis. Plants under physiological or environmental stress suffer losses in their photosynthetic capability through damage to photosystems and other cellular processes caused by reactive oxygen species (ROS). But certain Trichoderma strains activate biochemical pathways that reduce ROS to less harmful molecules. This and other mechanisms described here make plants more resistant to biotic and abiotic stresses. The net effect of these fungi’s residence in plants is to induce greater shoot and root growth, increasing crop yields, which will raise future food production. Furthermore, if photosynthesis rates are increased, more CO₂ will be extracted from the atmosphere, and enhanced plant root growth means that more sequestered C will be transferred to roots and stored in the soil. Reductions in global greenhouse gas levels can be accelerated by giving incentives for climate-friendly carbon farming and carbon cap-and-trade programmes that reward practices transferring carbon from the atmosphere into the soil, also enhancing soil fertility and agricultural production.     

Discontinuous gas exchange, water loss, and metabolism in Protaetia cretica (Cetoniinae, Scarabaeidae)

Insects are at high risk of desiccation because of their small size, high surface-area-to-volume ratio, and air-filled tracheal system that ramifies throughout their bodies to transport O(2) and CO(2) to and from respiring cells. Although the tracheal system offers a high-conductance pathway for the movement of respiratory gases, it has the unintended consequence of allowing respiratory transpiration to the atmosphere. When resting, many species exchange respiratory gases discontinuously, and an early hypothesis for the origin of these discontinuous gas exchange cycles (DGCs) is that they serve to reduce respiratory water loss. In this study, we test this "hygric" hypothesis by comparing rates of CO(2) exchange and water loss among flower beetles Protaetia cretica (Cetoniinae, Scarabaeidae) breathing either continuously or discontinuously. We show that, consistent with the expectations of the hygric hypothesis, rates of total water loss are higher during continuous gas exchange than during discontinuous gas exchange and that the ratio of respiratory water loss to CO(2) exchange is lower during discontinuous gas exchange. This conclusion is in agreement with other studies of beetles and cockroaches that also support the hygric hypothesis. However, this result does not exclude other adaptive hypotheses supported by work on ants and moth pupae. This ambiguity may arise because there are multiple independent evolutionary origins of DGCs and no single adaptive function underlying their genesis. Alternatively, the observed reduction in water loss during DGCs may be a side effect of a nonadaptive gas exchange pattern that is elicited during periods of inactivity.     

Meeting the challenge of food and energy security

Growing crops for bioenergy or biofuels is increasingly viewed as conflicting with food production. However, energy use continues to rise and food production requires fuel inputs, which have increased with intensification. Focussing on the question of food or fuel is thus not helpful. The bigger, more pertinent, challenge is how the increasing demands for food and energy can be met in the future, particularly when water and land availability will be limited. Energy crop production systems differ greatly in environmental impact. The use of high-input food crops for liquid transport fuels (first-generation biofuels) needs to be phased out and replaced by the use of crop residues and low-input perennial crops (second/advanced-generation biofuels) with multiple environmental benefits. More research effort is needed to improve yields of biomass crops grown on lower grade land, and maximum value should be extracted through the exploitation of co-products and integrated biorefinery systems. Policy must continually emphasize the changes needed and tie incentives to improved greenhous gas reduction and environmental performance of biofuels.     

Sustainable limits to crop residue harvest for bioenergy: maintaining soil carbon in Australia's agricultural lands

The use of crop residues for bioenergy production needs to be carefully assessed because of the potential negative impact on the level of soil organic carbon (SOC) stocks. The impact varies with environmental conditions and crop management practices and needs to be considered when harvesting the residue for bioenergy productions. Here, we defined the sustainable harvest limits as the maximum rates that do not diminish SOC and quantified sustainable harvest limits for wheat residue across Australia's agricultural lands. We divided the study area into 9432 climate‐soil (CS) units and simulated the dynamics of SOC in a continuous wheat cropping system over 122 years (1889 – 2010) using the Agricultural Production Systems sIMulator (APSIM). We simulated management practices including six fertilization rates (0, 25, 50, 75, 100, and 200 kg N ha^?1) and five residue harvest rates (0, 25, 50, 75, and 100%). We mapped the sustainable limits for each fertilization rate and assessed the effects of fertilization and three key environmental variables – initial SOC, temperature, and precipitation – on sustainable residue harvest rates. We found that, with up to 75 kg N ha^?1 fertilization, up to 75% and 50% of crop residue could be sustainably harvested in south‐western and south‐eastern Australia, respectively. Higher fertilization rates achieved little further increase in sustainable residue harvest rates. Sustainable residue harvest rates were principally determined by climate and soil conditions, especially the initial SOC content and temperature. We conclude that environmental conditions and management practices should be considered to guide the harvest of crop residue for bioenergy production and thereby reduce greenhouse gas emissions during the life cycle of bioenergy production.     

Mechanisms of tracheal filling in insects

Insects exchange respiratory gases primarily using tracheal systems that are filled with gas. However, in different developmental and environmental circumstances, liquid can occupy the tracheal system, which can significantly impair its respiratory function. Insects therefore use a suite of mechanisms for tracheal filling, which is the process of replacing tracheal liquids with gas. We review these mechanisms for liquid removal and gas filling. By integrating recent molecular work with older physiological literature, we show that liquid removal likely involves active ion transport in the whole tracheal system. Gas filling reveals fascinating interactions between geometry, surface chemistry of the tracheal walls, the tracheal liquid, and dissolved gases. The temporal proximity to moulting allows for potentially complex interdependencies between gas filling, moult‐associated hormone signaling, and cuticle sclerotization. We propose a mechanistic model for tracheal filling. However, because the composition of the liquid is unknown, it remains hypothetical.     

Global harmonization in the care and use of laboratory animals for the space life science research]

Space researches are supported with the international space agencies, NASA and NASDA. Animal experiments on the space life science must conform to the NIH policies and the NASA guide for the care and use of laboratory animals. The goal of the NIH policies is to promote the humane care of animals used biomedical and behavioral research, teaching, and testing. In each institute, the Institutional Animal Care and Use Committee (IACUC) plays an important role in conformity with NIH policies. The IACUC is charged with developing, recommending and monitoring NIH/NASA (ARC and KSC) policies, guides and rules relating to animal acquisition, care and use. In ARC and KSC, investigators will be responsible only for activities directly related to the conduct of their animal experiments. Even if researchers have protocols of the space science in Japan, the animal experiment should be carried out under the global harmonized conditions in accordance with NIH policies and NASA guides.     

Estimation of cardiac output by analysis of respiratory gas exchange.

Cardiac output is estimated by least squares fitting of a model of pulmonary gas exchange to measurements of respiratory gas composition obtained with a mass spectrometer during a rebreathing maneuver. This new technique estimates cardiac output on spontaneously breathing subjects at rest and requires neither central venous nor arterial blood samples. Principal features of the technique are the use of multiple gases simultaneously in the analysis, the use of a mathematical model for breath-to-breath evaluation of gas exchange, and simultaneous estimation of gas exchange and alveolar gas tensions with the same instrumentation. The technique is compared with thermal dilution estimates in dogs before and during hemorrhagic shock. Two-thirds of these estimates were within 20% of one another. The standard deviation of replication was 15%. Shortcomings, possibilities for improvement, and possible applications are discussed.     

Conducting airway gas exchange: diffusion-related differences in inert gas elimination.

We studied CO2 and inert gas elimination in the isolated in situ trachea as a model of conducting airway gas exchange. Six inert gases with various solubilities and molecular weights (MW) were infused into the left atria of six pentobarbital-anesthetized dogs (group 1). The unidirectionally ventilated trachea behaved as a high ventilation-perfusion unit (ratio = 60) with no appreciable dead space. Excretion of higher-MW gases appeared to be depressed, suggesting a MW dependence to inert gas exchange. This was further explored in another six dogs (group 2) with three gases of nearly equal solubility but widely divergent MWs (acetylene, 26; Freon-22, 86.5; isoflurane, 184.5). Isoflurane and Freon-22 excretions were depressed 47 and 30%, respectively, relative to acetylene. In a theoretical model of airway gas exchange, neither a tissue nor a gas phase diffusion resistance predicted our results better than the standard equation for steady-state alveolar inert gas elimination. However, addition of a simple ln (MW) term reduced the remaining residual sum of squares by 40% in group 1 and by 83% in group 2. Despite this significant MW influence on tracheal gas exchange, we calculate that the quantitative gas exchange capacity of the conducting airways in total can account for less than or equal to 16% of any MW-dependent differences observed in pulmonary inert gas elimination.     

The use of life-cycle assessment to evaluate the environmental impacts of growing genetically modified, nitrogen use-efficient canola

Agriculture, particularly intensive crop production, makes a significant contribution to environmental pollution. A variety of canola ( Brassica napus ) has been genetically modified to enhance nitrogen use efficiency, effectively reducing the amount of fertilizer required for crop production. A partial life-cycle assessment adapted to crop production was used to assess the potential environmental impacts of growing genetically modified, nitrogen use-efficient (GMNUE) canola in North Dakota and Minnesota compared with a conventionally bred control variety. The analysis took into account the entire production system used to produce 1 tonne of canola. This comprised raw material extraction, processing and transportation, as well as all agricultural field operations. All emissions associated with the production of 1 tonne of canola were listed, aggregated and weighted in order to calculate the level of environmental impact. The findings show that there are a range of potential environmental benefits associated with growing GMNUE canola. These include reduced impacts on global warming, freshwater ecotoxicity, eutrophication and acidification. Given the large areas of canola grown in North America and, in particular, Canada, as well as the wide acceptance of genetically modified varieties in this area, there is the potential for GMNUE canola to reduce pollution from agriculture, with the largest reductions predicted to be in greenhouse gases and diffuse water pollution.     

Effect of Cyclic Variations in Gas Exchange under Constant Environmental Conditions on the Ratio of Transpiration to Net Photosynthesis

Simultaneous cyclic variation in rates of both net photosynthesis and transpiration were induced in attached leaves of cotton and pepper plants under constant environmental conditions. The cyclic variations in photosynthesis and transpiration were found to be in phase, and the ratio net photosynthetic rate/transpiration rate remained constant over a wide range of gas exchange rates. A similar constancy of this ratio was also found as gas exchange rates declined following excision of a sunflower leaf, which was not initially cycling, in air. These results suggested that change in stomatal aperture was the only controlling factor involved and that it was affecting both processes proportionately. Visible loss of leaf turgur and measurable water stress developed in both pepper and cotton at peak exchange rates, but the gas exchange ratio remained constant. The failure of water stress and increased stomatal aperture to lower the gas exchange ratio suggested an absence of any significant leaf mesophyll resistance (r′_m) to inward diffusion of CO₂. The possibility that r′_m was low is discussed generally, and in relation to the use of chemical antitranspirants to raise the gas exchange ratio. Within the limits of the experiments, water stress apparently had no direct adverse effect on rates of net photosynthesis. The gas exchange ratio did not rise as exchange rates declined. Ultimately, at very low exchange rates, the ratio fell, declining to zero in cotton, but not in pepper. This decline was attributed to the onset of significant gas exchange through the cuticle, which was apparently less permeable to CO₂ than to water vapour. Positive net cuticular photosynthesis therefore probably does not occur in cotton. Except at very low exchange rates, the gas exchange ratio was higher in cotton than in pepper; it was similar in sunflower and cotton.     

Improving crop productivity and resource use efficiency to ensure food security and environmental quality in China

In recent years, agricultural growth in China has accelerated remarkably, but most of this growth has been driven by increased yield per unit area rather than by expansion of the cultivated area. Looking towards 2030, to meet the demand for grain and to feed a growing population on the available arable land, it is suggested that annual crop production should be increased to around 580 Mt and that yield should increase by at least 2% annually. Crop production will become more difficult with climate change, resource scarcity (e.g. land, water, energy, and nutrients) and environmental degradation (e.g. declining soil quality, increased greenhouse gas emissions, and surface water eutrophication). To pursue the fastest and most practical route to improved yield, the near-term strategy is application and extension of existing agricultural technologies. This would lead to substantial improvement in crop and soil management practices, which are currently suboptimal. Two pivotal components are required if we are to follow new trajectories. First, the disciplines of soil management and agronomy need to be given increased emphasis in research and teaching, as part of a grand food security challenge. Second, continued genetic improvement in crop varieties will be vital. However, our view is that the biggest gains from improved technology will come most immediately from combinations of improved crops and improved agronomical practices. The objectives of this paper are to summarize the historical trend of crop production in China and to examine the main constraints to the further increase of crop productivity. The paper provides a perspective on the challenge faced by science and technology in agriculture which must be met both in terms of increased crop productivity but also in increased resource use efficiency and the protection of environmental quality.     

White on green: under-snow microbial processes and trace gas fluxes through snow,Niwot Ridge,Colorado Front Range

The importance of snow and related cryospheric processes as an ecological factor has been recognized since at least the beginning of the twentieth century. Even today, however, many observations remain anecdotal. The research to date on cold-lands ecosystems results in scientists being unable to evaluate to what extent changes in the cryosphere will be characterized by abrupt changes in local and global biogeochemical cycles, and how these changes in seasonality may affect the rates and timing of key ecological processes. Studies of gas exchanges through snow have revealed that snow plays an important role in modulating wintertime soil biogeochemical processes, and that these can be the driving processes for gas exchange at the snow surface. Previous research has primarily focused on carbon dioxide, and resulted from episodic experiments at a number of snow-covered sites. Here we report new insights from several field sites on Niwot Ridge in the Colorado Rocky Mountains, including a dedicated snow gas flux research facility established at the 3340 m Soddie site. A novel in situ experimental system was developed at this site to continuously sample trace gases from above and within the snowpack for the duration of seasonal snow cover. The suite of chemical species investigated includes carbon dioxide, nitrous oxide, nitrogen oxides, ozone, and volatile inorganic and organic gases. Wintertime measurements have been supplemented by soil chamber experiments and eddy covariance measurements to allow assessment of the contribution of wintertime fluxes to annual biogeochemical budgets. This research has resulted in a plethora of new insight into the physics of gas transport through the snowpack, and the magnitude and the chemical and biogeochemical processes that control fluxes at the soil-snowpack and the snow-atmosphere interface. This article provides an overview of the history and evolution of this research, and highlights the findings from the ten articles that constitute this special issue.     

Mass spectrometry for monitoring respiratory and anesthetic gas waveforms in rats

A method is presented for real-time monitoring of airway gas concentration waveforms in rats and other small animals. Gas is drawn from the tracheal tube, analyzed by a mass spectrometer, and presented as concentration vs. time waveforms simultaneously for CO2, halothane, and other respiratory gases and anesthetics. By use of a respiratory simulation device, the accuracy of mass spectrometric end-tidal CO2 analysis was compared with both the actual gas composition and infrared spectrophotometry. The effects of various ventilator rates and inspiration-to-expiration ratios on sampling accuracy were also examined. The technique was validated in male Sprague-Dawley rats being ventilated mechanically. The difference between the arterial PCO2 (PaCO2) and the end-tidal PCO2 (PETCO2) was not significantly different from zero, and the correlation between PETCO2 and PaCO2 was strong (r = 0.97, P less than 0.0001). Continuous gas sampling for periods up to 5 min did not affect PaCO2, PETCO2, or airway pressures. By use of this new method for measuring end-tidal halothane concentrations in rats approximately 6.5 mo of age, the minimum alveolar concentration of halothane that prevented reflex movement in response to tail clamping was 0.97 +/- 0.04% atmospheric (n = 14). This mass spectrometric technique can be used in small laboratory animals, such as rats, weighing as little as 250 g. Gas monitoring did not distort either PETCO2 or PaCO2. Under the defined conditions of this study, accurate and simultaneous measurements of phasic respiratory concentrations of anesthetic and respiratory gases can be achieved.     

Insect eggs exert rapid control over an oxygen-water tradeoff

In terrestrial environments, the exchange of respiratory gases exacts a water cost: obtaining oxygen or carbon dioxide requires losing water. Insect eggs should be especially sensitive to this tradeoff-because they are unable to forage for water, have high surface area-to-volume ratios, and experience large temperature-driven changes in oxygen demand. Previous work from our laboratory, on eggs of a common hawk-moth, Manduca sexta, has shown that, during development, metabolic rate and water loss rates rise in parallel. These correlative data suggest that eggshell conductance increases to accommodate increasing metabolic demand. Here, we test this idea experimentally by subjecting eggs of M. sexta to 15, 21 (normoxia) and 35% oxygen for 24h, while measuring rates of metabolism (as carbon dioxide emission) and water loss. Hypoxia depressed egg metabolic rates, but led to pronounced, rapid increases in water loss. By contrast, hyperoxia had no significant effect on metabolism or water loss. These data demonstrate that insect eggs actively participate in balancing oxygen gain and water loss, and that they use tissue oxygen status, or some correlate of it, as a cue for increasing eggshell conductance. Rapid control over conductance may allow eggs to conserve water during an initial period of low metabolic demand, thereby deferring water costs of respiratory gas exchange until late in development.     

Diffusion-related differences in elimination of inert gases from the lung

Partial pressures of intravenously infused acetylene, Freon 22, and isoflurane (gases with similar solubilities in blood but differing molecular weights) were compared in arterial and mixed venous blood and mixed expired gas of 13 anesthetized mongrel dogs to determine whether gas molecular weight influenced gas exchange. Analysis of covariance was used to account for the variables of ventilation-perfusion ratio, partition coefficient, and experimental run before individual gas effects were sought. A gas effect difference was observed such that the arterial fractional retention of isoflurane (mol wt 184.5) would be 12% higher than that of acetylene (mol wt 26) if the two gases had identical partition coefficients. This effect was neither significantly increased by positive end-expiratory pressure nor decreased by high-frequency oscillatory ventilation. To test whether the individual gas effect was greater with gases with disparate erythrocyte and plasma partition coefficients, the exchange of ethyl iodide (erythrocyte-to-plasma solubility ratio 8.1) and diethyl ether (solubility ratio 0.95) was compared in five dogs. A larger difference between the elimination of the two gases was observed than predicted from the differences in molecular weight. The observed individual gas effect appears to be diffusion related, influenced both by the molecular weight of a gas and its erythrocyte-plasma partition coefficient ratio.     

Using network connectance and autonomy analyses to uncover patterns of photosynthetic responses in tropical woody species

Daily courses of leaf gas exchange and chlorophyll fluorescence in forest gap and understorey environments were used to build photosynthetic networks in two pioneers and two late-successional species. Photochemical and gas exchange networks were linked to each other by the relationship between electron transport rate and net CO₂ assimilation. Global network connectance (Cg), which represents the mean strength of connections within a given network, was calculated in the photochemical and gas exchange networks for both functional groups and environments. Autonomy in relation to environmental fluctuations was estimated considering the mean correlation between environmental and physiological data. Cg was consistently higher in plants under gap condition. High daily-amplitude of environmental variables in the gap induced strong connectance in photochemical and gas exchange networks regardless of functional group. Gap scenario demands network modulation with higher level of control than understorey, which would be attained by strong connections among components of photochemical and gas exchange networks. This would allow fine and fast tuning adjustments when facing highly variable and demanding environmental conditions throughout a day. As a consequence of this highly variable environment, both functional groups showed lower autonomy in the gap, where higher coupling between leaf physiology and environmental fluctuations was evident. Our results suggest that high plant–environment coupling demands high network connectance. Contrastingly, Cg was lower (especially in photochemical network) under forest understorey, promoting autonomy in a more stable environment. Our results indicate that there is a conservative pattern of photosynthesis control based on network modulation and environmental coupling. This suggests that changes in network connectance may not be specific of a functional group but rather a more general response to environmental fluctuations, strongly related to system stability. We consider this information crucial in understanding how complex adaptive systems deal with environmental fluctuations.